nTMS-Based DTI Fiber Tracking of Motor Pathways

Diffusion Tensor Imaging (DTI) fiber tracking allows for a tridimensional reconstruc-tion of main white matter fascicles, including the corticospinal tract (CST). Neverthe-less, standard DTI fiber tracking (DTI-FT) is limited by the fact that is based on the selection of anatomical landmarks as seeding region of interests (ROIs) for tract com-putation. This reduces the reliability and reproducibility of DTI-FT results, especially in brain tumor patients, in which the neural plasticity induced by the tumor itself causes a reorganization of the motor network resulting in a mismatch between ana-tomical and functional landmarks. Navigated transcranial magnetic stimulation (nTMS) provides a reliable mapping of the functional organization of the motor cortex that can be successfully used as seeding ROI for the DTI computation of the CST, im-proving the reliability and accuracy of the DTI-FT of the CST as compared to the standard DTI technique. Moreover, it provides the somatotopic organization of the CST, especially improving the visualization of fiber bundles connected to the motor cortical representation of arm and face muscles.